Efficiency estimation and payback periods The impact for industrial electric motor users
Summary This white paper discusses why efficiency est im at ion is im portant ; the param eters that can affect efficiency readings and how these measurem ents once obtained can be used to the advantage of a motor management specialist .
SKF @ptitude Exchange
SKF Reliability Systems
5271 Viewridge Court
San Diego, CA 92123
United States
tel. +1 858 496 3400
fax +1 858 496 3511
email: [email protected] Internet: http://www.aptitudexchange.com
BI09001
Nate Brooks and Adan
Reinosa
24 Pages Published October, 2009
Efficiency estimation and payback periods
© 2009 SKF Group
Efficiency estimation and payback periods
© 2009 SKF Group 2(24)
Table of contents
1. About the authors............................................................................................................3 2. Abstract .............................................................................................................................3 3. Introduction ......................................................................................................................3 4. The “ins and outs” of efficiency......................................................................................4 4.1. Electrical input..................................................................................................................4 4.2. Voltage balance................................................................................................................5 4.3. Voltage distortion.............................................................................................................6 4.4. Current level .....................................................................................................................8 5. Effective service factor ....................................................................................................8 6. Load...................................................................................................................................9 7. Energy assessment..........................................................................................................9 8. Efficiency details............................................................................................................ 10 9. What does this mean to motor health, life, and cost to companies?..................... 11 9.1. Payback Period Calculation ......................................................................................... 11 10. Efficiency Estimation and Payback Period................................................................. 12 10.1. Equations ....................................................................................................................... 12 10.2. Assumptions .................................................................................................................. 12 10.3. Calculations.................................................................................................................... 13 11. Measuring Efficiency..................................................................................................... 21 12. Applying more Efficient Motor Findings..................................................................... 21 13. Summary ....................................................................................................................... 22
14. ............................................. 23References/Standards and Related Information
Efficiency estimation and payback periods
© 2009 SKF Group 3(24)
1. About the authors
This article was written by Nate Brooks,
Sales Representative for Baker Instrument
Company, and Adan Reinosa, Efficiency
Solutions - New Technologies for the Los
Angeles Dept. of Water and Power.
Baker Instrument Company is an SKF
Group company.
2. Abstract
The ability to understand and calculate the
efficiency of an electrical motor is vital in
respect to energy conservation, cost
savings, and reduced emissions. Industrial
customers require this information for
applications such as power conversion,
conveyer belt motors and water pumps to
name a few. Having a method in which to
obtain this efficiency calculation, as well as
to identify key concerns for improving
efficiency in the field is essential to running
a successful, safe and efficient operation.
On December 19th, 2007, President
George W. Bush signed into law the Energy
Independence & Securities Act of 2007.
This law, which goes into affect on
December 19th, 2010, states the
mandatory minimum efficiency level for
motors is designated by the NEMA
Premium Efficiency® Program. Included in
this program are all motors previously
covered under the Energy Policy Act of
1992 plus the following list: motor ratings
1-200Hp (including u-frame), Design C,
close looped pump , footless, vertical shaft-
normal thrust, 8-pole and polyphase
motors. Also required by this law are those
motors ranging from 200-500Hp in the
Design B Class. These motors must meet
the requirements as stated in NEMA MG-1
Table 12-11.
This white paper discusses why efficiency
estimation is important; the parameters
that can affect efficiency readings and how
these measurements once obtained can be
used to the advantage of a motor
management specialist.
3. Introduction
So what is Efficiency? Merriam and
Webster Dictionary define Efficiency as a
noun created in 1633. 1: the quality or
degree of being efficient or 2: a: efficient
operation b (1): effective operation as
measured by a comparison of production
with cost (as in energy, time, and money)
(2): the ratio of the useful energy delivered
by a dynamic system to the energy supplied
to it. WIKIPEDIA.com describes it as follows.
The efficiency of an entity (a device,
component, or system) in electronics and
electrical engineering is defined as useful
power output divided by the total electrical
power consumed (a fractional expression).
Efficiency = Useful power output
Total power input
The real question is why is this important?
In today’s market, prices are going up while
the value of the dollar has declined. Global
warming is causing a concern for the health
of our environment, bringing high taxes
and fines for companies that don’t maintain
clean and efficient work places. Also with
high numbers of corporate mergers, losses
Efficiency estimation and payback periods
© 2009 SKF Group 4(24)
of highly trained personnel and sufficient
time for effective monitoring and diagnoses
of plant parameters have diminished. These
issues are further impeded with the fact
that nearly 60% of all electrical power used
in the industrial sector, is consumed by
electric motors. Throw in higher
maintenance costs, production costs, and
personnel costs and year end profits suffer.
As a motor maintenance professional your
job is to ensure that the plant stays running
safely and smoothly. However, industry
wide, responsibilities have been added,
causing increased stress and require
greater skill sets. Saving company money
by the use of the most efficient motors and
taking advantage of rebates provided by the
federal government and local power
companies has been included in the job
description of most maintenance
professionals.
4. The “ins and outs” of
efficiency
As described, efficiency is the ratio of a
motor’s mechanical output to its electrical
input. However, what affects this ratio, and
why are each of these factors important to
motor maintenance professionals?
4.1. Electrical input
The power condition of a motor, i.e. the
quality of power delivered to a motor is
comprised of the voltage level, unbalance,
and distortion. The voltage at 100% rated
load is typically found labeled on the
nameplate of the motor. In an ideal
condition voltage would be 100% with 0%
unbalance and distortion. However, motors
operate in the real world and often can be
found running with anywhere from 5-10%
over or under voltage. Under voltage is
described as the condition when the
average terminal voltage is below full load
nameplate voltage. Over voltage is the
exact opposite, described as the average
terminal voltage above the nameplate
voltage. Note here that it was stated
“terminal voltage” not voltage displayed at
the panel meters of the motor control
cabinet (MCC). If the leads from the MCC
are long, then there typically is an
appreciable voltage drop across them;
causing the operating voltage of the motor
to be lower than the voltage measured at
the MCC’s. This is the key to understanding
why voltage plays into efficiency.
Power as they say is as easy as Pie, where
P(power)=I(current)*E(voltage). If the
voltage is lower than expected, current will
increase to balance the equation, resulting
in additional heat stresses felt on a motor.
This additional heat causes the winding
insulation deteriorate more rapidly, thereby
reducing the life of a motor. NEMA and
EASA suggest a general rule of thumb, that
for every 10°C of additional heat to the
windings, the motor’s insulation life is
reduced by half.
Operating with over voltages is a common
cause for excessive harmonic current
generation. This is the reason for a drop of
the operating power factor, which may be a
cause for power factor penalties. If the
voltage level is sufficiently high, the motor
will drop the operating efficiency, causing
the heat in the motor to increase. An
increased level of stator current can
Efficiency estimation and payback periods
© 2009 SKF Group 5(24)
produce severe overheating in a motor,
resulting in increased copper loss (I2R). Bad
over voltage conditions are far less
hazardous to the motor than under voltage
conditions. According to NEMA MG1, Part
12, Page 20: “AC induction motors shall
operate successfully up to plus / minus 10%
of rated voltage, with rated current.”
Other factors that affect the level of voltage
are speed and torque, during transients.
The lower the voltage level the higher the
expected slip will be for a given load. With
torque, the lower the voltage, the lower the
torque will be. In some instances, i.e. rotor
bar issues, reversible motors, and VFD
driven motors, the torque may not be
sufficient enough to allow for the motor to
stay in motion. The majority of panel
meters have the average buss voltage
across all 3 phases. Each individual phase
voltage is generally not displayed.
4.2. Voltage balance
According to NEMA MG-1, Voltage Balance
is defined as the maximal deviation from
the average line voltage, divided by the
average line voltage. The higher this
voltage unbalance percentage the higher
your current unbalance will be in response,
once again leading to additional induced
heat. NEMA MG-1 also states: “The
currents at normal operating speed with
unbalanced voltages will be greatly
unbalanced in the order of approximately 6
to 10 times the voltage unbalance.”
According to the EPRI study “Voltage Power
Quality Issues, Related Standards &
Mitigation Techniques: Effect of Unbalanced
Voltage on End Use Equipment
Performance”, 34% of US distribution
systems operate with a voltage unbalance
exceeding 1%. This point is in reference to
distribution systems only, which means at
the point of common coupling entering the
industrial facility. Hence, the chances are
that clearly more than 34% of motor
voltage busses are exceeding the 1%
allowed by NEMA’s MG-1.
Other effects caused by Voltage Unbalance
include increased torque ripple, decreased
locked-rotor and startup torques, increased
level of vibrations, slightly reduced speeds
and increased temperatures.
In vibration, the negative sequence voltage
introduced by voltage unbalance elevates
the vibration level at multiples of two times
the electrical fundamental frequency. A
good goal in industrial environments is to
attempt to keep voltage unbalance below
the 1% level for all motors. Experience at
Baker Instrument Company, an SKF Group
Company shows that voltage unbalance
and poor motorload matches are among
the most common electrical problems
found in the field.
Also, take into consideration the stresses
induced from VFD’s and other components
that generate internal harmonics on a
motor. If only voltage, current and load
levels are monitored, the maintenance
professional may be led to believe that the
motor is running in good standing (green)
with no abnormal heat stress. However,
when voltage unbalance and distortion
percentages are taken into account, there
may be unnecessary heat induced into that
motor.
Efficiency estimation and payback periods
© 2009 SKF Group 6(24)
4.3. Voltage distortion
Voltage distortion is the amount of voltage
at fundamental frequency, compared to the
total voltage at all other frequencies. Any
distortion in the voltage signal creates
currents in the motor that do not
significantly contribute to the generation of
torque. On the contrary a large portion of
these additional currents within the motor
slow the rotor down and act as an electrical
break to the system. These currents are
responsible for additional heating. The
amount of voltage distortion sent to the
motor by the power source is smaller than
the amount of current distortion that it
causes. This means that a relatively small
amount of voltage distortion creates a
larger amount of current distortion and
heat. Other parameters affected by voltage
distortion are speed, torque, and vibration.
The speed tends to decrease with a higher
voltage distortion. The torque band
increases slightly for higher levels of
distortion. With vibration, voltage distortion
increases the noise levels, in particular
multiples of the 60 Hz fundamental and
can often be heard audibly. Power factor is
also affected due to the fact that pf is
composed of both displacement and
distortion power factors. The distortion pf
decreases with higher %THDv, which
decreases the overall power factor. Total
Harmonic Distortion (THDv%) is defined by
the following equation:
%THDv=100. Vdist
Vfund
Where:
Vdist. is the voltage distortion (all
components other than the fundamental)
Vfund. is the fundamental voltage (50Hz or
60Hz for line operated motors)
The %THDv is a very common value in field
instrumentation. NEMA MG-1 specifies the
use of HVF (Harmonic Voltage Factor) and
percent voltage unbalance for calculating
the derating factor. This is calculated with a
different equation beyond the scope of this
paper; however, Figure 1 the curves that
are used in this calculation are shown.
Figure 1. Harmonic voltage factor curves
Percentage NEMA derating is the total
derating caused by poor power condition. A
few quick tips for troubleshooting and
spotting power condition problems are that
they typically are generated from the
Efficiency estimation and payback periods
© 2009 SKF Group 7(24)
upstream power distribution system (i.e.
voltage source). A problem felt on one
motor will be seen on all motors related to
that particular buss. These stresses are
particularly detrimental to motors
operating at higher loads or with more
frequent cycle times.
Looking at the overall motor performance
the user must consider all the issues
directly related to the probable overheating
of a motor. A motors performance in this
instance can be defined by the current level
and effective service factor. Common
reasons for over heating of a motor can be
found at the motor control cabinet (MCC) by
looking at the current level, the quality of
the voltage and the operating load level.
Poor motor performance conveys reasons
for excessive stress in the motor. Excessive
heat generated by this performance will
destroy the insulation system, causing
premature electric motor failure. Motor
performance issues can either be avoided
by properly diagnosing and correcting the
root cause of the stress, or they can be
mitigated so that future motor operation
does not need to change to avoid
shortening the motor’s life. Motor
performance problems frequently are a
combination of up-stream and down-
stream issues. Motor performance
problems rarely affect the whole voltage
buss. When solving performance problems,
it is important to understand where the
root cause of the problem is located. Figure
2 displays a representation of how various
factors affect a motor. This diagram is
handy for troubleshooting mechanical and
electrical issues.
Figure 2. How various factors affect a motor
If the condition is created mainly due to
over load, then the operation of the motor
has to be changed. If the condition is
caused by a poor power condition, then the
Efficiency estimation and payback periods
© 2009 SKF Group 8(24)
power quality of the supply has to be
enhanced. Mitigation of motor performance
problems is possible, by managing the
thermal issues. Additional chilling, or force
cooling of a motor are measures that can
bring the operating temperature back into
the design limits, without requiring a
change to the load or power conditions.
These types of measures will raise the life
expectancy of the motor back into
acceptable levels.
4.4. Current level
Current Level is defined as the highest line
current delivered to the motor, and is a
common focal point when discussing added
heat concerns. Motors are designed to
operate long term at maximum nameplate
current. Current level is one of the
characteristic responses of the motor to a
given combination of the overall power
condition and load. Sometimes it is found
that current level is defined as the average
current level for all phases. For predictive
maintenance reasons; however, the highest
line current developed is of a much larger
importance, since heat is one of the main
degradation mechanisms for insulation.
The heat in each winding depends to the
amount of the current through that
particular winding. Hence, the weakest
point to the motor’s insulation with respect
to current level has to be identified as the
phase with the largest current. Current
level is influenced by the level of load,
voltage level, voltage unbalance, and the
voltage distortion. During line startup, the
motor is exposed to typically 6 to 10 times
the rated current. This process is cause for
severe heating, and should be avoided
unless necessary. Soft starts, Delta-Wye
starters or wound motors are common
additions to an electrical system that aide in
diminishing the deteriorating influence of
frequent startups. With respect to severe
over currents, NEMA MG1 states:
“Induction motors while running and at
rated temperature shall be capable of
withstanding a current equal to 150% of the
rated current for 30 seconds”.
With respect to some special type of DC
generators, NEMA MG1 also specifies:
“These generators shall be capable of
carrying, (...)
a) 115% of rated current continuously (...)
b) 125% of rated current for 2 hours (...)
c) 200% or rated amperes for 1 minute
(...)”
Similar specifications can be frequently
obtained regarding allowable overload and
over current conditions for induction
motors. This type of information can be
obtained from motor manufacturers.
5. Effective service factor
When all of the aforementioned issues
discussed previously are combined, they
affect the calculation called effective service
factor. Effective service factor, a Baker
Instrument Company derived equation, is
defined as %Load divided by %NEMA
derating. Motors are designed to operate
with a maximal thermal stress. Operating
at temperatures higher than that quickly
reduces the life of the motor. Insulation
failure is imminent if the motor is operated
Efficiency estimation and payback periods
© 2009 SKF Group 9(24)
under temperatures that are too high.
Factors that can increase the temperature
in a motor are high ambient temperatures,
operating at higher elevations, restricted
airflow, high load requests, poor supplied
power quality, broken rotor bars, poor
terminal contacts, etc. The most frequently
encountered scenario for thermal
overloading are due to either load, or a
combination of load with a poor power
condition.
6. Load
Load is defined as the domain that uses the
motor as a sensor to look at the driven
load. The question to be asked is whether
the motor load is sufficiently low so that the
poor power condition does not affect the
motors healthy. Load level problems are
always caused by the load. The motor
reacts, and tries to deliver the torque that
the load requires.
From a predictive maintenance standpoint,
the really important issue is up time, which
is not limited to just motor health. Load
condition monitoring is a new aspect that
online monitoring offers. Load level and
load signature are the tools of choice to
further understand the motor load system.
This tool is offered by Baker Instrument
Company, an SKF Group Company’s torque
monitoring software (T3000). In these
cases, refer to the NEMA derating curves.
The graphs in Figure 3 both display how
much a motor has to be derated if the
voltage condition is of a certain quality.
Just like with motor conditions effective
service factor problems are frequently a
combination of up-stream and down-
stream issues. These problems rarely affect
the whole voltage bus. When solving
effective service factor problems it is
important to understand where the root
cause of problem is located. Mitigation of
effective service factor problems is also
possible, by managing the thermal issues
identified. Once again, if the condition is
created mainly due to over load, then the
operation of the motor has to be changed.
If the condition is caused by a poor power
condition, then the power quality of the
supply has to be enhanced.
7. Energy assessment
Energy assessment is a review of all issues
relevant to energy and efficiency. With
rising energy costs, increasing operating
efficiency is becoming of more importance.
In order to perform good energy
assessment, one must be able to answer
the following questions. Are my motors
running efficiently? Is it worth it for me to
exchange this motor for a higher efficiency
one? Should I wait until the next necessary
repair of this efficient motor before I
exchange it? Where has this motor been
before? Has it been repaired? How efficient
would a motor of X design run at Y% Load?
Efficiency identifies whether a NEMA class
motor operates at similar efficiencies as a
comparable, healthy motor could under
normal conditions. With Baker Instrument
Company’s Explorer Series tester,
EfficiencyD:\Program Files\Baker
Efficiency estimation and payback periods
© 2009 SKF Group 10(24)
Instrument\MotAna\help\Energy
Assessment\Efficiency.htm compares the
motor under test to a database containing
NEMA designed motors that look for
matches in rating, number of poles and
voltage level. It interpolates available motor
data to the load level measured in the field,
and compares the operating efficiency to
the one that the database identifies.
Operating Efficiency of a motor can not be
easily measured in a field application.
Relevant standards of IEEE, IEC, JEL and
similar organizations have a number of
requirements which commonly can only be
fulfilled in a laboratory environment. These
standards also usually concentrate on
ensuring a proper description of a motor’s
capabilities under good operating voltage
conditions. In the field, however, there is
little room for requirements like uncoupling
a motor or regulating the voltage level for a
saturation run. Questions regarding a
particular motor’s capabilities are found to
be secondary in importance when
compared to the operating efficiency under
given conditions in the field. The result of
such an environment is that true
efficiencies, as defined by IEEE, IEC, or JEL
are unrealistic to obtain.
Operating efficiencies, however, are of
crucial importance to energy conscious
management. Requirements for true
measurements of operating efficiencies in
field environments are ample and
unrealistic. They can include installing
torque transducers on the shaft of the
motor, and measuring the input power to
the motor at the motor terminals
frequently at high voltage levels. Instead of
a true efficiency measurement, efficiency
estimation becomes the only field friendly
approach for energy management. The
difference between operating efficiency
measurement and operating efficiency
estimation is that the former attempts to
find the true operating efficiency via direct
measurement, while the latter accepts a
small measure of inaccuracy for severely
increased user friendliness. It is important
to note that different motor designs
operate with different efficiencies.
8. Efficiency details
Advances in motor design, motor
manufacture and legislation requirements
are the most important reasons for higher
efficiencies in newer motors. Load levels
below 50% will typically show lower
efficiencies. Current level increases with
lower voltage levels, which tends to
decrease the efficiency. Commonly a motor
running at rated voltage, or only slight over
voltages, will show the highest efficiency.
Voltage unbalance increases the average
current only mildly, but the losses in one or
more of the phases are substantial. This
causes the efficiency to drop drastically.
Current level increases strongly with mild
increases in voltage distortion, equating
higher currents to lower efficiencies.
Broken rotor bars or endrings cause the
motor to need more slip for delivery of the
required torque. This has the effect of
additional current in the stator, which also
decreases the operating efficiency. Motors
operating at low efficiencies are burning up
larger amounts of heat in losses. This does
not automatically mean that these motors
Efficiency estimation and payback periods
© 2009 SKF Group 11(24)
will run hotter. Older motor designs, for
example, include larger fans for additional
heat reduction. Unfortunately this causes
additional losses from friction and windage
created by these larger fans. Newer motor
designs frequently allow the motor to
operate under higher temperatures, since
the quality of the insulation material has
improved with respect to older motors. This
allowed the motor designers to additionally
increase the efficiency of the motors by
decreasing the amount of cooling and
windage loss with a smaller fan. For any
motor; however, any reason causing it to
operate at lower efficiencies is reason for
expecting higher operating temperatures,
and lower life due to insulation
deterioration.
9. What does this mean to motor
health, life, and cost to
companies?
As stated previously there are many factors
that can affect the health and longevity of a
motor. The list of problems that has been
discussed in the white paper is just a
portion of what can occur. A overwhelming
number of issues can cause the efficiency
of motors to drop and the cost of power
consumption to increase. So how is the cost
of replacing inefficient motor or repairing
process to increase efficiency calculated in
terms of payback.
9.1. Payback Period Calculation
Payback Period is a simple payback
calculation identifying motors that could be
exchanged for more efficient motors at a
monetary gain. Payback Period takes the
values obtained as a target efficiency and
subtracts the values of the operating
efficiency. The difference can be considered
as wasted energy points. With the
knowledge of how many hours per day and
days per week the motor is run, the $ per
kWh, and shelf price for the replacement
motor, it is then possible to identify a
straight payback period. Plant managers
require a good working knowledge of
operating efficiencies. The root causes of
low efficiencies (i.e. poor motors, power
condition, or load mismatches) must be
known and scrutinized. It is not worth the
time or effort to solve a case with very low
efficiency, if the motor is operating safely
but only for few hours per day. The
payback period of such an application would
be exceedingly high. Payback period
identifies whether the motor load
application under test is worth
investigation. It compares the list price of
the motor with the potentially energy cost
savings for motors under normal under
normal operation and target efficiencies.
Low loads are sources of poor power
factor, and low efficiencies. Unless there
are clear reasons for doing otherwise,
loading of 75% to 100% is viewed as optimal
for efficiency. Below is a chart that was
made possible by research and help from
SIMMCO, Larry Zaring and John Holmes of
Integrated Power Services, Mike Renfro of
US Motors, Robert B. Boetler and Adan
Reinosa at the Los Angeles Department of
Water and Power Energy & Efficiency
group.
Efficiency estimation and payback periods
© 2009 SKF Group 12(24)
10. Efficiency Estimation and Payback Period
10.1. Equations
• Motor Run Cost per year( $/yr) = hp * L * 0.746 * hr * C * (100/Estd)
• Annual Savings = hp * L * 0.746 * hr * C (100/Estd - 100/Eee)
• Annual kWh used = hp * L * 0.746 * hr * (100/Estd)
• Simple Payback (yrs) = (Price Premium + Installation Cost - Utility Rebate) / Annual Savings
• hp = Horsepower rating of Motor
• L = percentage of Full load / 100
• 0.746 = conversion from hp to kW
• hr = hours of run time, for this case study we will use 3000 hrs to simulate a motor that is
run for ~ 5 days a week for 10 hours a day and 8000 hrs to simulate a motor run 24/7
• C = $/kWh, for this study we used $0.10/kWh
• Estd = the efficiency of the motor currently installed
• Eee = the efficiency of a higher quality premium efficiency motor
10.2. Assumptions
Installation cost = $88.00/hour/person or $1350/day for 12 hours.
John Holmes of SIMMCO said typically he sees ~$1800/install $ 1,800.00
US Motors 200hp General Purpose ODP Premium Efficient D200P2C (96.2%) $ 1 0,044.00
US Mtrs 500hp Titan General Purpose TEFC Premium Efficiency C500P2W (95.4%) $ 59,106.00
DOE Rebate $ 3,000.00 DOE Rebate $ 7,500.00
Utility Rebate for 200hp $ 5,922.00 Utility Rebate 500hp $30,453.00
Since the utility rebate (LADWP's current proposal) is 50% of the project cost then the top
portion of the simple payback equation will always be the same as the rebate.
Based on the average US fuel Mix the amount of CO2 emitted (in Lbs) per 1 kWh gnerated = 1.5
Based on the average US fuel Mix the amount of NOx emitted (in Lbs) per 1 kWh gnerated = 0.004
Based on the average US fuel Mix the amount of SO2 emitted (in Lbs) per 1 kWh gnerated = 0.008
200 /
500 HP Mtr
75% of full load $0.10 / kWh 80%, 85%, 90% and 95% efficiencies are
actual running mtr efficiency
3000 / 8000
runtime hours
Efficiency estimation and payback periods
© 2009 SKF Group 13(24)
10.3. Calculations
Legend
Type of motor
Typical motor efficiency used
High efficiency motor
Table 1. Motor cost to run per year
Efficiency estimation and payback periods
© 2009 SKF Group 14(24)
Table 2. Annual savings
Table 3. Annual kWh used
Efficiency estimation and payback periods
© 2009 SKF Group 15(24)
Table 4. CO2 emmission generated (in lbs)*
* Based on the US average fuel mix, ~1.5lbs of CO2 is emitted per kWh generated.
(Side note- 1 acre of forest will consume 30 tones of CO2 per year)
Table 5. Nox Emission Generated (in lbs)**
** Based on the US average fuel mix, ~0.004Lbs of Nox is emitted per kWh generated.
Table 6. SO2 Emission Generated (in lbs)***
***Based on the US average fuel mix, ~0.004Lbs of SO2 is emitted per kWh generated.
Efficiency estimation and payback periods
© 2009 SKF Group 16(24)
Table 7. Annual kWh saved
Table 8. Time to payback with government proposed $15 hp rebate (in years)
Efficiency estimation and payback periods
© 2009 SKF Group 17(24)
Table 9. Time to payback with Utility Rebate Only (in years)
Table 10. Total time to payback both rebates combined (in years)
Efficiency estimation and payback periods
© 2009 SKF Group 18(24)
Table 11. CO2 emissions reduction (in lbs) - due to replacement of inefficient motor
Table 12. NOx emissions reduction (in lbs) - due to replacement of inefficient motor
Efficiency estimation and payback periods
© 2009 SKF Group 19(24)
Table 13. SO2 emissions reduction (in lbs) - due to replacement of inefficient motor
Efficiency estimation and payback periods
© 2009 SKF Group 20(24)
Table 14. Possible Scenario based on say the City of Los Angles: this is a complete
assumption just to show enormity of this issue.
As shown, even with the use of generalities, i.e. 75% full load, 3000 or 8000 per year run time
hours, $0.10/kWh, and a rough average of install cost, even a small motor consumes a lot of
power and costs a great deal. Now replace a inefficient motor, upgrade it to a premium
efficiency motor. The energy savings are tremendous but also the gains can be substantial.
Less maintenance downtime spent repairing or replacing broken or breaking motors, less
money spent on emergency repairs, more production time and products being built, overall
increases to the quality of life and greater efficiency and profits for the company.
Efficiency estimation and payback periods
© 2009 SKF Group 21(24)
11. Measuring Efficiency
There are many ways in which to calculate
the efficiency of a motor; however, some
are cumbersome, and others are
completely intrusive and out of the question
when it comes to real world scenarios. A
paper written by Oregon (OSU) and
Washington (WSU) State Universities titled
“A Laboratory Assessment of In-Service
and Non-Intrusive Motor Efficiency Testing
Methods” covers these methods in detail.
For further clarification on laboratory
testing please refer to “3 Phase Induction
Motor Field and Laboratory Efficiency
Testing” written by Ernesto Wiedenbrug,
Ph.D., SM IEEE.
When it comes to efficiency field estimation
there are currently 4 test methods utilized
today that are considered non-intrusive.
Note the word estimation. Some degree of
inaccuracy is expected as a price to pay for
an in-service field test over a no load un-
coupled laboratory test on a dynamometer.
These tests are the Nameplate method,
Upper-Bound with Resistance method,
ORMEL 96 and the Instantaneous Current
Method. The Baker Instrument Companies,
an SKF Group Company’s EXP3000 tester
uses the Instantaneous Current Method.
This method requires a measurement of
the motors input power and a calculated
estimate of the motors output power.
Current transformers and potential
transformers are utilized to gather
incoming rotating voltage and currents for
all 3- phases. Then calculations are made
based on these values for speed and
torque. Air gap torque is calculated using
the Park’s Vector (or 2-Axis) Theory.
Friction, stray load and windage losses are
estimated and then subtracted from the air
gap torque calculation to get an estimate of
the output torque. As was mentioned
efficiency is the ratio of the mechanical
output to electrical input. Since speed does
not require a physical measurement taken
near or on the motor, it is estimated
through the gathered currents and
voltages. All data can be gathered safely
from the motor’s control cabinet (MCC),
making this a highly non-intrusive method
to test for efficiency. Also in the study done
by WSU and OSU, the findings for all test
methods showed the fact that
instantaneous current method does not try
to estimate losses; but rather the output
power. It is less sensitive to the efficiency of
the predicted motor. This means it has a
smaller margin of error on estimating
lower end efficiencies, making it not only a
good non-intrusive test method but also a
highly accurate test method.
12. Applying more Efficient Motor
Findings
Once it has the operating efficiency, the
EXP3000 extracts a comparable efficiency
from a motor database which contains over
22000 different NEMA design motors of
numerous motor manufacturers. The
percentage difference in the losses between
the tested motor and a comparable motor
(target efficiency) is then evaluated with
respect to the thresholds. There are a few
Efficiency estimation and payback periods
© 2009 SKF Group 22(24)
organizations available today that have a
listing of these NEMA prescribed motors as
well as methods in how to go about
selecting the right motor. MotorMaster+ is
a third-party software tool for energy-
efficient motor selection and management.
The MotorMaster+ software was developed
by Best Practices, a program under the
U.S. Department of Energy’s Office of
Industrial Technologies. MotorMaster+ 3.0
software includes a catalog of over 20,000
AC motors. Version 3.0 features motor
inventory management tools, maintenance
log tracking, efficiency analysis, savings
evaluation, energy accounting, and
environmental reporting capabilities. It can
be obtained at no cost from the following
website:
http://www.energy.wsu.edu/cfdocs/mmdow
nload/register.cfm.
Motor Master+ is a standard application
utilized by the EXP3000. Another very
handy and well designed website can be
found at http://www.motorsmatter.org/.
This site offers a very useful 1-2-3 step
program that aides in the decision process
of buying, replacing, and managing motors.
In fact the title of one of their main books is
“The 1-2-3 Approach to Motor
Management - Users Manual”. Also
available for download is a spreadsheet that
can be used to check off steps in the 1-2-3
process.
13. Summary
In today’s society with the environmental
and economic needs, a more reliable, safe
and beneficial way to help the economy,
reduce energy demand, and stop global
warming is needed. The number one way
for the maintenance and motor
management group to aide in this goal is to
ensure that the motors, drive systems and
loads under their control are running as
efficiently and smoothly as possible. One
way to carry out this necessity is to
determine the efficiency of the motor and
correct issues with the surrounding system
that directly relate to, or affect, the motors
efficiency. Correcting issues, such as a
cavitating pumps, overcurrent situations,
and improperly tuned drives, can increase
the efficiency and life of the motor while
reducing the maintenance costs, down-
times, and production losses. To illustrate
again lets use a 200Hp motor running at
8000hrs per year at 85% efficiency. This
motor would:
1. Cost the facility $105,317.65 per year
to run (not including penalties for poor
power factor and any carbon tax paid),
2. The facility will use 1,053,176.47 kWh
per year on this motor, and
3. Cause approximately 790 Tons of CO2
to be produced and emitted into the
atmosphere.
Swapping this 85% efficient motor for a
NEMA Premium 96.2% efficient motor will
result in the following:
1. An annual energy savings of
$12,261.51, which by the end of the
first year more than pays for the motor
Efficiency estimation and payback periods
© 2009 SKF Group 23(24)
2. an annual kWh reduction of
122,615.14, thus reducing energy
demands
3. decreasing the CO2 buildup by roughly
91 Tons.
Due to utility rebates currently in existence
and the possibility of a government
introduced rebate program, the payback
period for this motor is approximately 8.6
months. Each associated year of use will
produce approximately $12,000 additional
cost savings that can be put to good use in
any number of ways. The necessity for
efficiency estimation and knowledge of
payback periods is an essential tool that
every motor management professional
should have at the ready in their tool bag.
For more information on this subject,
please contact Baker Instrument Company,
an SKF Group Company or the co-authors
of this white paper.
14. References / Standards and
Related Information
IEEE519. More information on power
condition standards can be found in IEEE
working groups under http://grouper.ieee.org/groups/
Electric Machines, G.R. Slemon and A.
Straughen, 0-201-07730-2, Addison-
Wesley Publishing Company, 1980
NEMA MG-1 1998
Energy Tips - Eliminate Voltage
Unbalance, U.S.Department of Energy
http://www1.eere.energy.gov/industry/bestprac
tices/pdfs/eliminate_voltage_unbalanced_motor
_systemts7.pdf
Instantaneous Torque as Predictive
Maintenance Tool for Variable Frequency
Drives and Line Operated Motors, Ernesto
Wiedenbrug Ph.D., SM IEEE., Baker
Instrument Company
Optimizing Electric Motor Systems at a
Corporate Campus Facility, U.S.
Department of Energy,
http://www.nrel.gov/docs/fy99osti/25998.p
df
Optimized Pump Systems Save Coal
Preparation Plant Money and Energy, U.S.
Department of Energy,
http://www1.eere.energy.gov/industry/best
practices/pdfs/peabody1.pdf
Motor System Upgrades Smooth the Way
to Savings of $700,000 at Chevron
Refinery, U.S. Department of Energy,
http://www.nrel.gov/docs/fy99osti/26057.p
df
United States Industrial Motor Systems
Market Opportunities Assessment,
U.S.Depeartment of Energy,
http://www1.eere.energy.gov/industry/best
practices/pdfs/mtrmkt.pdf
Buying an Energy-Efficient Electric Motor,
Motor Challenge (a program of the
U.S.Department of Energy), Sept 2006, http://www1.eere.energy.gov/industry/bestprac
tices/pdfs/mc-0382.pdf
Efficiency estimation and payback periods
© 2009 SKF Group 24(24)
Replacing an Oversized and Underloaded
Electric Motor, Motor Challenge (a program
of the U.S.Department of Energy), http://www1.eere.energy.gov/industry/bestprac
tices/pdfs/mc-2463.pdf
Optimizing Your Motor Driven System,
Motor Challenge (a program of the
U.S.Department of Energy), Sept 1996, http://www1.eere.energy.gov/industry/bestprac
tices/pdfs/mc-0381.pdf
Reducing Power Factor Cost, Motor
Challenge (a program of the
U.S.Department of Energy), Sept 1996, http://www1.eere.energy.gov/industry/bestprac
tices/pdfs/mc60405.pdf
Frequently asked questions on the Impacts
of the Energy Policy Act of 1992 on
Industrial End Users of Electric Motor-
Driven Systems Motor Challenge (a
program of the U.S.Department of Energy),
Sept 1996, http://www1.eere.energy.gov/industry/bestprac
tices/pdfs/e-pact92.pdf
Pulp and Paper Mills: Profiting from
Efficient Motor System Use,
U.S.Department of Energy, http://www.energystar.gov/ia/business/industry
/pulpmtr.pdf
The 1-2-3 approach to motor
management, Motor decisions matter
campaign, Consortium for Energy
Efficiency. http://www.motorsmatter.org/tools/123_manu
al.pdf
Baker Instrument Companies Explorer Help
File http://www.harbec.com/pdf/harbecforest.pdf